Organic molecules are the chemicals of life, compounds composed of more than one type of element, that are found in, and produced by, living organisms. The feature that distinguishes an organic from inorganic molecule is that organic contain carbon-hydrogen bonds, whereas inorganic molecules do not. The four major classes of organic molecules include carbohydrates, proteins, lipids and nucleic acids.
The term carbohydrates is actually a descriptor of what these molecules are composed of; “carbon hydrates,” in a ratio of one carbon molecule to one water molecule (CH2O)n.
The word saccharide is a handy synonym for carbohydrate, because it can be preceded with a prefix that indicates the size of the molecule (mono-, di-, tri- poly-).
Monosaccharides
- single sugars (one molecule)
- simplest
Disaccharides
- double sugars
- combination of two monosaccharides
Polysaccharides
- polymers composed of several sugars
- can be same monomer (many of same monosaccharide) or mixture of monomers
Proteins
Proteins are polymers composed of monomers called amino acids. Each amino acid contains contain a…
- base amino group ( -NH2)
- acidic carboxyl group ( -COOH)
- hydrogen atom
…all attached to same carbon atom (the α–carbon or alpha carbon). A fourth bond attaches α-carbon to a side group that varies among different amino acids. These side groups are important, as they affect the way a protein’s amino acids interact with one another, and how a protein interacts with other molecules.
Although there are hundreds of different amino acids, most organisms use only 21 to build proteins.
Peptide bonds are the covalent bonds which link amino acids together into chains, like the beads on a necklace. A dipeptide is 2 amino acids linked together, a polypeptide, more than two.
Lipids are molecules that are hydrophobic, not attracted to water because the non-polar covalent bonds linking carbon and hydrogen aren’t attracted to the polar bonds of water.
The four major groups of lipids include fats, phospholipids, waxes and steroids.
Fats
Fats and oils are made from two kinds of molecules:
- glycerol (a type of alcohol)
- three fatty acids (so known as triglycerides)
Phospholipids
The structure of this type of lipid includes a hydrophobic, “water hating,” hydrocarbon tails and hydrophilic, water loving phosphate groups on the end. This means that phospholipids are soluble in both water and oil.
Our cell membranes are made mostly of phospholipids arranged in a double layer with the tails from both layers facing inward and the heads facing outward (lipid bilayer).
Waxes
Waxes are esters of alcohol which are insoluble in water and difficult to break down. Wax forms protective and waterproof layers on some plants, bacteria, animal fur and integuments of insects.
Steroids
The central core of a cholesterol molecule, consisting of four fused rings, is shared by all steroids. Cholesterol is precursor to our sex hormones and Vitamin D. Our cell membranes contain a lot of cholesterol which helps to keep the membrane flexible and fluid even when our cells are exposed to cooler temperatures.
Nucleic acids are polymers made up of nucleotide monomers.
Nucleotides
Each monomer of nucleic acid is a nucleotide and consists of 3 portions:
- a pentose sugar
- one or more phosphate groups
- one of five cyclic nitrogenous bases
Nucleic Acid Structure
Nucleotides linked by covalent bonds between phosphate of one nucleotide and sugar of next, forming a phosphate-sugar backbone. The nitrogenous bases extend from it like teeth of a comb.
Hydrogen bonds form between specific bases of two nucleic acid chains, forming a stable, double-stranded DNA molecule. Hydrogen bonding twists the phosphate-deoxyribose backbones into a helix, thus typical DNA is a double helix.
ATP: The energy transfer molecule
Adenosine 5'-triphosphate (ATP) is a multifunctional nucleotide, most important as the "molecular currency" of intracellular energy transfer. ATP transports chemical energy within cells for metabolism.
Additional Organic Chemistry Resources
The website Science Prof Online and the page Organic Chemistry Help are excellent sources for more information on organic molecules.
Sources
Bauman, R. (2005) Microbiology.
Park Talaro, K. (2008) Foundations in Microbiology.
Tami Port - Tami Port is a college professor of cell and microbiology and creator of ScienceProfOnline.com, a free science education website.
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